From a search on the WEB, there are a lot of medical articles that mention using Numonics Electronic Graphics Calculator. From a 1982 NIH article on Nucleic Acids Research:

Quote:
The magnified image is then traced, along the top side of the viewing
screen, using a digitizer. The digitizer used in this system is a NUMONICS
GRAPHICS CALCULATOR which was chosen because it can be used with a back projected
image, is of sufficiently high accuracy and of reasonable cost. This
digitizer can resolve 0.025 cm over a working range of 59 cm x 59 cm. As the
tracing head is moved along the image, a stream of X-Y coordinates is accepted
by the computer at a rate of more than 100 coordinate pairs/sec via a BCD
interface.